Biochar e adubação potássica no crescimento e no estado nutricional de mudas de Pau-Rosa (Aniba Rosiodora Ducke.) em condições controladas

Abstract

In the Amazon region, Yellow Oxisols are characterized by high acidity, low natural fertility, and low cation exchange capacity, factors that limit the availability of essential nutrients for plant growth. In this context, biochar has been considered a promising alternative for mproving the chemical and physical properties of tropical soils, particularly when combined with mineral fertilization. This study evaluated the effects of biochar application and increasing rates of potassium chloride (KCl) on the growth and nutritional status of Aniba rosiodora Ducke (rosewood) seedlings cultivated in a dystrophic Yellow Oxisol under controlled conditions. The experiment was conducted in a greenhouse at Campus III of the National Institute for Amazonian Research (INPA), Manaus, Amazonas, Brazil, during 2025. A completely randomized design in a 5 × 2 factorial arrangement was adopted, consisting of two biochar rates (0 and 10 t ha⁻¹) and five KCl rates (0, 50, 100, 150, and 200 kg ha⁻¹), totaling ten treatments with six replicates each. Biometric evaluations were performed at 30, 60, 90, 120, 150, and 180 days after transplanting, measuring seedling height, stem diameter, and leaf number. At the end of the experiment, shoot and root dry biomass, the Dickson Quality Index (DQI), and leaf concentrations of macronutrients (P, K, Ca, and Mg) and micronutrients (Fe, Mn, Zn, and Cu) were determined. Biochar was the main factor responsible for the observed responses, promoting more pronounced increases in height growth, stem diameter growth, and DQI. The absolute height growth rate was approximately 68% higher in seedlings cultivated with biochar than in those grown without it. Likewise, DQI increased significantly in the presence of biochar, indicating the production of morphophysiologically more balanced seedlings. Regarding nutritional status, biochar was associated with higher leaf concentrations of Ca, Mg, Fe, Mn, and Cu, while also promoting greater nutritional balance for K and P. A significant interaction between biochar and KCl rates was observed for potassium, demonstrating that the conditioner altered the dynamics of fertilizer uptake and utilization by the seedlings. Zinc was the only micronutrient whose leaf concentration decreased in the presence of biochar, a response likely associated with the adsorption of Zn²⁺ onto the reactive surfaces of the carbonized material. The isolated application of KCl produced only limited effects on biomass-related variables, a pattern consistent with the physiological adaptation of the species to naturally oligotrophic environments. Overall, the combination of biochar with intermediate KCl rates resulted in more balanced nutritional and morphophysiological responses. These findings indicate that the application of biochar at a rate of 10 t ha⁻¹ represents a potentially viable strategy for improving the quality of rosewood seedlings produced in low-fertility substrates of the Central Amazon.